A conventional analog telephone service is a voice band-limited service adapted such that audio frequency components higher than 3.4 kHz are suppressed to be transmitted. End users communicate with others generally within the limited band. IP telephony services using VoIP technology are also made compatible with connections to a conventional analog telephone network or to traditional telephone subscriber sets to accomplish telecommunications services generally within the aforementioned limited voice band.
Such an IP telephony service over an IP (Internet Protocol) network is however possibly provided which is free from the restriction of the conventional analog telephone service, i.e. limiting the frequency components higher than 3.4 kHz, and transmits voice signals in a wideband (with its bandwidth of 3.4 KHz or more) to increase the quality of service for communication services (hereinafter, referred to as “high-quality IP telephony service”).
However, in order to provide such a high-quality IP telephony service as a payable service that is acceptable to customers, the problems described below arise from the viewpoints of satisfaction to the customers, and therefore a business model that would justify charging the customers has been difficult to build.
Specifically, when an end user originates a call from his or her IP telephone subscriber set on an IP network supporting the high-quality IP telephony service, the telephone subscriber set of a called party is identified by the phone number specified by the calling end user. When the calling end user dials a phone number, he or she may usually not be aware of whether or not the telephone set corresponding to the dialed phone number is compatible to the high-quality IP telephony service. Resultantly, it is occasional for the calling party, and hence determined afterwards, whether or not the called party will enjoy a chargeable high-quality IP telephony service subscriber. In this situation, it is difficult to get acceptance from the called party in every case.
For example, when a dialed phone number is the phone number of an ordinary telephone set on a public switched network supporting the analog telephone service, the telephone service is provided such that the voice frequency components higher than 3.4 kHz are suppressed so as to be of substantially the same quality of service as the analog telephone service. By contrast, when a dialed phone number is the phone number of an IP telephone set on an IP telephone network supporting the high-quality IP telephony service, the user will enjoy the high-quality IP telephony service on broadband voice signals. In those examples, the former applies a free service in the service quality comparable to the analog telephone service, whereas the latter does a toll service in the high-quality IP telephony service.